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INFLUENCE OF CERTAIN ELEMENTS ON STEEL.               359
hearth steel is of the same character, and this will he sufficient proof that the best of steel may contain a considerable proportion.    If, therefore, it appears from a set of experiments that copper exerts a bad effect, then one of two things follows: .   (1) The experiments have left some factor out of the question.
(2) The maker of good steel has some trick by which he overcomes the enemy.
It would be a cause for satisfaction if we could boast that the latter supposition were true, but we have never known that copper injured the cold properties of steel in any way, and no system has been devised to obviate its'influence. Hard and soft steels of our manufacture have found their way into all channels! of trade, and although many failures have come, as they have everywhere, from high carbon, high manganese, or high phosphorus, there have been no cases where it was necessary to invoke the aid of copper. This fact outranks and transcends in value any limited series of tests that might be given. In the same way there is no evidence that copper segregates, experience pointing rather to perfect uniformity.
Steel may contain up to one per cent, of copper without being seriously affected, but if at the same time the sulphur is high, say .08 to .10 per cent., the cumulative effect is too great for molecular cohesion at high temperatures and it cracks in -rolling. This tearing occurs almost entirely in the first passes of the ingot, so that it is of little importance to the engineer who is concerned only with perfect finished material. In the purest of soft steels containing not more than .04 per-cent, of either phosphorus or sulphur, the influence of even; .10 per cent, of copper may be detected in the less ready welding of seams during; the process of rolling, but ordinarily when the sulphur is below ..05 per cent, the copper injures the rolling quality very little, even in the proportion of' .75 per cent. In all cases the cold properties seem to be unaffected.
The only facts ever brought out against copper, as far .as I am aware, are in a paper by Stead,* who shows that steels containing from 0.46 to 2 per cent, of copper do not give good results in drawn wire when a high percentage of carbon is also present, but it is stated that there is nothing to show that .rails or plates are affected injuriously.                        . .
The quantitative effect of copper upon the tensile strength was
* Jour. I. and S. I., Vol. II, 1901, p. 122.        '.                          ~~~